An analytie model of phyllotaxis

We discuss a model for phyllotaxis which is sufficiently simple to allow analytical insight in the system. We describe generic properties of the solutions. Among other things we show that the symmetry breaking which characterizes phyllotaxis has the features of a second order phase transition.Nous discutons un modèle de phyllotaxie. Celui-ci est suffisamment simple pour permettre une approche analytique du système. Nous décrivons plusieurs propriétés génériques des solutions ; la phyllotaxie se caractérise notamment par une brisure de symétrie : nous montrons que celle-ci présente toutes les caractéristiques d'une transition de phase de seconde espèce

Funzione renale durante ventilazione a pressione positiva continua a bassa frequenza con scambio extracorporeo di CO2.

Six lambs anesthetized, paralyzed, tracheostomized and cystostomized were ventilated alternatively with continuous positive pressure ventilation (CPPV), at 16 breaths per min (bpm) and with LFPPV-ECCO2R, at 2 bpm. The renal function, as measured by urinary flow, creatinine clearance, osmolar clearance, and osmolar output, improved between 25% and 35%, lowering the respiratory rate from 16 to 2 bpm, at the same positive end expiratory pressure. The possible mechanism involved (antidiuretic hormone, hemodynamic factor, cardiopulmonary reflex) is discussed

Association between hippocampal structure and serum Brain-Derived Neurotrophic Factor (BDNF) in healthy adults: A registered report

The hippocampus is a highly plastic brain structure supporting functions central to human cognition. Morphological changes in the hippocampus have been implicated in development, aging, as well as in a broad range of neurological and psychiatric disorders. A growing body of research suggests that hippocampal plasticity is closely linked to the actions of brain-derived neurotrophic factor (BDNF). However, evidence on the relationship between hippocampal volume (HCV) and peripheral BDNF levels is scarce and limited to elderly and patient populations. Further, despite evidence that BDNF expression differs throughout the hippocampus and is implicated in adult neurogenesis specifically in the dentate gyrus, no study has so far related peripheral BDNF levels to the volumes of individual hippocampal subfields. Besides its clinical implications, BDNF-facilitated hippocampal plasticity plays an important role in regulating cognitive and affective processes. In the current registered report, we investigated how serum BDNF (sBDNF) levels relate to volumes of the hippocampal formation and its subfields in a large sample of healthy adults (N = 279, 160 f) with a broad age range (20–55 years, mean 40.5) recruited in the context of the ReSource Project. We related HCV to basal sBDNF and, in a subsample (n = 103, 57 f), to acute stress-reactive change in sBDNF. We further tested the role of age as a moderator of both associations. Contrary to our hypotheses, neither basal sBDNF levels nor stress-reactive sBDNF change were associated with total HCV or volume of the dentate gyrus/cornu ammonis 4 (DG/CA4) subfield. We also found no evidence for a moderating effect of age on any of these associations. Our null results provide a first point of reference on the relationship between sBDNF and HCV in healthy mid-age, in contrast to patient or aging populations. We suggest that sBDNF levels have limited predictive value for morphological differences of the hippocampal structure when notable challenge to its neuronal integrity or to neurotrophic capacity is absent. © 202

Risposte emodinamiche durante ventilazione a pressione positiva continua a bassa frequenza con rimozione extracorporea di CO2 (LLFPPV-ECCO2R.) : studio comparativo rispetto alla ventilazione a pressione positiva continua (CPPV)

Six lambs, where extracorporeal blood flow ranging between 600 and 1000 ml min-1 was continuously maintained, were mechanically ventilated in two different modes: continuous positive pressure ventilation (CPPV) with 5 cm H2O PEEP and low frequency positive pressure ventilation with 5 cm H2O PEEP and extracorporeal CO2 removal through a carbon dioxide membrane lung (LEPPV-ECCO2R). The blood gases were in normal ranges through both CPPV and LFPPV-ECCO2R, even if a higher PaO2 was found during CPPV. However, during LFPPV-ECCO2R, cardiac output increased about 30%, O2 transport 19.3%, while heart rate, pulmonary artery pressure and arterial pressure did not change. LFPPV-ECCO2R, in the experiments, seems to overcome some hemodynamic impairments of CPPV